A fibrous polymer represented by triacetyl cellulose (hereinafter referred to as "TAC") or a polyester polymer such as polyethylene terephthalate (hereinafter referred to as "PET") are generally used as the support for photographic materials.
In general, photographic materials are in the form of sheet film as X-ray film, plate-making film and cut film or roll film as in color or black-and-white negative roll to be mounted in a cartridge having a width of 35 mm or less.
TAC, when used as the support for roll films, exhibits a high transparency and an excellent decurlability after development.
On the other hand, PET films are excellent in mechanical strength and dimensional stability but remain curled when unwound after development. This poor handleability puts restrictions on its application range despite its excellent properties.
In recent years, photographic materials have been used for a variety of applications, for example, the reduction in the size of cameras, the increase in the film delivery speed upon picture taking and the increase in the magnification. This requires a support having a high strength, a good dimensional stability and a small thickness.
Further, the reduction in the size of cameras accompanies a further demand for smaller cartridges.
In order to miniaturize the cartridge, three problems need to be solved.
One of the three problems is to inhibit the reduction in the dynamic strength accompanied by the reduction in the thickness of the film.
The second problem is that a strong curl develops with time during storage, due to the reduction in the size of the spool.
The third problem is a reduction in the processing aptitude, such as the punching property, which occurs due to the decrease in the dynamic strength of the film. In order to improve the dynamic strength, particularly the elastic modulus to further accelerate thinning, it is common to increase the orienting magnification in case of a biaxial oriented film and raise the crystallinity. However, the resulting film is fragile and liable to cleave. In particular, there is a possibility of generating punching dust in the punching process.
In order to reduce the curl of polyester film a method has been known as disclosed in U.S. Pat. No. 4,141,735 and JP-A-51-16358 (The term "JP-A" as used herein means an "unexamined published Japanese patent application").